Power controllers are well known and normally employ analog techniques. Digital techniques are normally avoided where smooth control is desired, for example, in controlling the dimming gas discharge lamps such as fluorescent lamps in an electronic ballast.
The present invention provides a novel digital implementation for power control circuits, particularly for the control of fluorescent lamp dimming.
Some limitations on analog power control systems are:
I. Inflexible Driving Algorithm
Optimal driving of power switches (MOSFETs, bipolar, transistors, thyristers, IGBTs and the like) requires complex algorithms based on non-linear multiple stage and variable functions, with a variety of predetermined parameters being chosen as the circuitry's physical parameters change.
For example, in the case of a fluorescent ballast power controller, flexible algorithms are desired to supply special loads when:
a) a complex working regime for fluorescent lamps including the preheat startup operation is needed.
b) Non-linear or special operation requirements for the fluorescent lamp complying to its V/I working curve, and as a function of the dimming decision table to provide the best operation at all light levels.
c) Flexibility to enable use of different lamp configurations (types and numbers of lamps) and different main voltages.
II. The number of electronic circuits increases as number of control function increases. If silicon implementation is feasible, it requires a large silicon overhead.
III. No Decision Tables
An analog solution does not provide “IF-THEN” decisions. It only provides “YES-NO” decisions using analog comparators and only linear predetermined algorithms. For example: voltage controlled oscillator (VCO) for frequency modulation (FM) or pulse width modulation (PWM) zero to max., pulse control, etc.
IV. No Parameters Set Tables
This has to do with different lamp configurations, in the case of a fluorescent lamp ballast, but also with many other decisions made by the controller in every state of its operation. One specific example is the time response of the lamp current loop being different at high level or low level as well as during transient or at steady state operation.